After 76 minutes of the rugby test, Fitzgerald, who was sitting in the west stand, stripped off and leaped over the barrier.
He made it past stewards on to the playing surface, through the in-goal area and "attempted to mount the goal post", the court heard.
Fitzgerald's naked jaunt only came to an end when he was tackled by security guards.
The referee was forced to stop the game for a minute, Mr Hamilton said.
When spoken to by police, Fitzgerald said the streak was "just for laughs".
He was less candid outside court today when he told the ODT he "probably shouldn't" comment.
Ms Taylor-Cyphers asked Judge Dominic Flatley not to enter a conviction against her client's name.
A discharge without conviction hearing will be heard next month.
The court heard Fitzgerald had a clean criminal record but had previously received diversion over an assault.
According to the University of Otago website, the defendant is an assistant research fellow at the Centre for Sustainability.